Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps. The one or more pumps draw fuel from the fuel tank and deliver pressurized fuel to one or more primary fuel loads and to one or more secondary fuel loads via one or more supply lines. Generally, the primary fuel loads, which include the fuel manifolds in the engine combustor, are supplied with fuel via, for example, a priority flow line. The secondary fuel loads, which may include a motive flow valve and regulator, one or more variable geometry actuators, and one or more bleed valves, are supplied with fuel via, for example, a secondary flow line.
The priority flow line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include at least a metering valve and a pressurizing valve. The metering valve is typically configured to control priority flow to the one or more primary fuel loads. The pressurizing valve, which is typically disposed downstream of the metering valve, functions to maintain a minimum system pressure magnitude in portions of the supply lines. More specifically, the pressurizing valve typically maintains pump discharge backpressure above a minimum pressure magnitude.
In some systems, when the one or more secondary fuel loads are being supplied with fuel, the minimum pump discharge backpressure may need to be higher than what is needed for a given priority flow level. One solution to this is to maintain the minimum pump discharge backpressure at the higher level at all times to accommodate the secondary flow requirements. This solution, however, may exhibit certain undesirable drawbacks. For example, this solution can make the scheduling of priority flow difficult during engine start up. This solution may also generate excessive fuel system heat, and may increase horsepower consumption by the one or more pumps.
Hence, there is a need for a system and method of controlling gas turbine engine fuel pressurization that does not cause difficulty in the scheduling of priority flow during engine start up and/or does not result in excessive fuel system heat generation and/or does not increase horsepower consumption by the one or more fuel pumps. The present invention addresses one or more of these needs.